1. Field of the Invention
The present invention relates to a method for packaging an optical part such as an optical isolator, a wavelength multiplexer, an optical coupler, and a collimator, and in particular, to an optical part packaging method which can improve characteristics of an optical part in temperature and tensile strength.
2. Description of the Related Art
Reliability of optical fiber parts, fine optical parts, and optical waveguide parts generally depends on their packaging reliability. Packaging refers to fixing an optical fiber, and metal or plastic housings for protecting optical components, implemented in two stages: fixing a first housing after arranging the components, for a specific function; and fixing a second housing for attaching an external label of a fabricated optical part thereon and increasing the reliability of the optical part. The are numerous means and methods for fixing optical fibers end-to-end and a few of these are depicted by U.S. Pat. No. 5,097,524 to Alexander Wasserman et al. entitle Optical Fiber Termination, U.S. Pat. No. 5,418,876 to Hsin Lee entitled Fiber Optic Connector With Epoxy Preform; U.S. Pat. No. 5,212,745 to Calvin M. Miller entitled Fixed And Temperature Tuned Fiber Fabry-Perot Filters, U.S. Pat. No. 4,406,515 to Harold A Roberts entitled Fiber Optic Connector, and U.S. Pat. No. 4,258,977 to Helmut H. Lukas entitled Optical Fibre Connector.
Here, a collimator assembly method and a collimator-including optical part packaging method will be described.
The collimator is an optical system for converting light emitted from a fine light source to a parallel light or converging transmitted parallel light, using variations on the wave front of light caused by a lens. A collimator has an optical fiber tube for retaining an optical fiber, a ferrule for supporting the optical fiber tube and the optical fiber, a lens for focusing light emitted from the optical fiber, and a sleeve for fixedly aligning the lens with the ferrule.
In a conventional collimator assembly method, the coating of the optical fiber tube is peeled off to expose the optical fiber retained therein. Then, the optical fiber tube and the optical fiber are coated with an adhesive on the surfaces thereof, and fixedly inserted into the center of the ferrule. Then, the ferrule is coated with the adhesive on a surface portion thereof, and fixedly inserted in the sleeve. The lens is aligned with the ferrule, coated with the adhesive on diametrically opposite ends thereof, and fixedly inserted into the sleeve.
Then, a pair of collimators are aligned in a package housing, wherein a first housing is fixed around both collimators by a plurality of solder joints to fix the collimators and protect the optical devices thereof. That is, the first housing is fixed around the sleeves by the solder joints. Then, a second housing is fixed around the first housing by the adhesive, for attaching an external label thereon and increasing the mechanical strength of the first housing. Protection tubes are fixed to the collimators by an epoxy sealing to protect the ends of the optical fibers from an external environment, with the brims of the protection tubes connected to both brims of the second housing. Thus, the collimators are completely packaged.
However, the above conventional optical part (collimator) packaging method has distinct problems. The reliability of the optical part is lowered due to temperature changes, vibration, shock, and tensile force, in a long term, because the optical components are fixed in the collimators by a fixing material (adhesive or solder), and the collimators are packaged. Further, the sleeves are fixed to the first housing by soldering, and the temperature of the first housing exceeds at least 100.degree. during soldering, thus varying characteristics of the fixing material (adhesive or solder) and remarkably decreasing the reliability of the optical parts. In addition, vibration and moisture are easily introduced into the collimators because the first and second housings are fixed by the fixing material. As a result, the optical devices are highly vulnerable to breakage, and their optical characteristics are degraded.